A vertical type stirrer or agitator 101 as shown in FIG. 5 is used in the production of fermented products such as, for instance, fermented drinks. This stirrer 101 has a motor-supporting frame 103 set up on a tank shell 102 forming a fermentation tank, a motor (with a reducer, etc.) 104 mounted on the top of the motor-supporting frame 103, and a rotary shaft or stirrer shaft 106 connected to the motor 104. Shaft 104 is supported in a free-rotating state by motor-supporting frame 103 by means of a bearing 105. Shaft 104 extends down inside tank shell 102 and is held vertically in the fermentation tank inner space 107. Shaft 104 is constituted so that agitation propellers 108, 108 mounted at the lower end thereof agitate a treatment material to enhance fermentation in tank inner space 107.
This type of fermentation stirrer 101 is designed so as to prevent fermentation gases generated in tank 107 from leaking out by providing an appropriate shaft seal apparatus 109 between rotary shaft 106 and a rotary shaft penetrating portion 102a of tank shell 102.
Some known types of shaft seal apparatus 109 installed on this type of stirrer 101 are equipped with a single or double end-face contact mechanical seal while others are provided with grand-packings.
The type of shaft seal apparatus equipped with a single mechanical seal (hereinafter referred to as "the first prior art apparatus") has a seal case in the rotary shaft penetrating portion 102a in which a stationary seal ring on the seal case is pressed against a rotary seal ring on the rotary shaft 5. Thus, in the first prior art apparatus, tank inner space 107 is sealed by a sliding contact between the two seal rings rotating relative to one another.
The end-face contact type shaft seal apparatus provided with a double mechanical seal (hereinafter called "the second prior art apparatus") has a pair of mechanical seals, of the same type of the first prior art apparatus, arranged side by side. A sealing fluid region is thus formed between the pair of mechanical seals and keeps the tank inner space 107 air-tight. The sealing fluids used in this type of apparatus include oils and liquids that would cause no problems if they leak into the tank. The type of shaft seal apparatus using oil as sealing fluid is additionally provided with an oil unit where the oil is circulated so as to keep the oil from leaking into the tank inner space from the seal region. This type of shaft seal apparatus is also designed so that the pressure of the oils and liquids (that would cause no problems if they leak into the tank) can be held higher than that inside the tank, to prevent the gas inside the tank (i.e., the fermentation gas) from leaking out into the seal region.
The type of apparatus using a grand-packing (hereinafter name "the third prior art apparatus") has a stuffing box installed in the rotary shaft penetrating position 102a and a number of grand packings, generally braided packings, are arranged side by side in the space between the stuffing box and the rotary shaft 106 to seal the tank inner space 107. Also, a lantern ring is usually provided in the middle of the group of grand-packings, where nitrogen gas is fed.
Rotary equipment such as the aforesaid fermentation stirrers 101, when used with pharmaceuticals, foodstuffs, raw materials to be processed into pharmaceuticals and foodstuffs, and other such materials, require strict hygienic control. They are subjected to sterilization treatment periodically or as necessary by the injection of a sterilization gas, usually high-temperature steam, into the tank inner space 107. In this sterilization treatment, parts of the shaft seal apparatus that face the tank inner space 107 cannot be cleaned well by the sterilization gas which is jetted into the tank alone. Therefore, the same gas is directly jetted onto those parts of the shaft seal apparatus.
In the first and second prior art apparatuses, however, the seal end faces on both sides which are in contact with each other cannot be well sterilized by the jetting of the sterilization gas. Especially in the second prior art apparatus, which is of complicated construction, the sterilization gas cannot reach many parts of the apparatus, which results in grossly insufficient sterilization. Another problem is that since those prior art apparatuses are based on end-face contact type mechanical seals, dust will arise from the contact wearing of the two end faces in operation, which can fall into the tank inner space 107. It is difficult, therefore, to achieve sufficient hygienic control in the tank. The problem with the first prior art apparatus is that the gas in the tank cannot be shut out completely. Toxic or odiferous gases in the tank could contaminate or otherwise damage the environment.
The third prior art apparatus also presents the following problems. The grand-packings cannot be cleaned enough even by jetting a sterilization gas directly at them. Furthermore, the grand-packings produce dust from contact with the rotary shaft 106 in operation, and that dust can fall into the tank inner space 107. For those reasons, sufficient hygienic control in the tank inner space 107 is difficult to effect, as with the first and second prior art apparatuses.
As set forth above, the first through third prior art apparatuses cannot be well-sterilized by hygienic procedures including treatment by jetting sterilization gas. They are accordingly not suitable for use in rotary equipment where strict sanitation is required. The industry would benefit if those problems were addressed.